Slope detector for indicating flat tires and the like

Abstract

A device for detecting a change in the slope of a member relative to a reference is disclosed. The device includes a slope sensor, mounted to the member, characterized by a resistance between one end of the slope sensor and an intermediate node, and a conductive fluid within the sensor which varies the effective resistance of the slope sensor between the end thereof and the node by an amount corresponding to the change in the slope of the member relative to the reference.

I claim: 
     
       1. In a vehicle having an axle and an inflatable tire disposed at each end of the axle, a device for detecting when one of the tires becomes underinflated, comprising: a slope detector, mounted to the axle, including a curved chamber, an electrically conducting fluid partly filling the chamber, and a resistance element disposed in the chamber in partial contact with the fluid, said resistance element characterized by a resistance between one end of the element and an intermediate node which varies in a predetermined manner with the position of the fluid in the chamber;   means for damping the flow of the fluid to reduce the rate of change of the resistance of the detector caused by movement of the axle and thereby to render the detector substantially insensitive to axle vibration associated with road travel; and   means responsive to the resistance of the detector for detecting variations in the slope of the axle.   
     
     
       2. The device of claim 1 wherein the damping means includes a surface of the curved chamber adapted to contact the surface of the conductive fluid to frictionally retard motion of the fluid. 
     
     
       3. The device of claim 1 wherein the chamber is adapted to confine the conducting fluid to a substantially uniform cross-sectional area to damp the flow of the fluid. 
     
     
       4. The device of claim 3 wherein the cross-sectional area of the confined fluid is about three-one hundredths of a square inch and the conducting fluid includes mercury. 
     
     
       5. The device of claim 1 wherein the chamber is curved in a substantially circular arc. 
     
     
       6. In a vehicle having first and second axles and an inflatable tire disposed at each end of each of the axles, a device for detecting when one of the tires becomes underinflated, comprising: a plurality of slope detectors, one of the slope detectors mounted on each of the axles, each of the slope detectors including a curved chamber, an electrically conducting fluid partially filling the chamber, and a resistance element disposed in the chamber in partial contact with the fluid, said resistance element having a resistance between one end of the element and an intermediate node which varies in a predetermined manner with the position of the fluid in the chamber;   means for damping the flow of the fluid to reduce the rate of change of the resistance of each of the slope detectors caused by movement of the axles and thereby to render the detectors substantially insensitive to axle vibration associated with road travel;   comparator means responsive to the resistances of the first and second slope detectors for generating a signal corresponding to the imbalance between the slope of the first axle and the slope of the second axle;   alarm means for activating an alarm in response to the signal generated by the comparator means;   delay circuit means for preventing the alarm means from activating the alarm until the signal generated by the comparator means has persisted for a predetermined time interval; and   means for resetting the delay circuit means upon termination of the signal generated by the comparator means, whereby signals corresponding to temporary imbalance caused by movement of the axles are substantially prevented from activating the alarm.   
     
     
       7. The device of claim 6 wherein the delay circuit means includes means for varying the predetermined time interval in response to the magnitude of the imbalance in slope between the first and second axles, whereby the time interval is made shorter for larger differences in slope. 
     
     
       8. The device of claim 6 wherein the chamber of each of the slope detectors is adapted to confine the conducting fluid to frictionally retard movement of the conductive fluid and thereby the damp the response of the slope detector. 
     
     
       9. The device of claim 8 where the cross-sectional area of each of the chambers is about one-thirty-second of a square inch and the conducting fluid includes mercury. 
     
     
       10. The device of claim 6 wherein the chamber of each of the slope detectors is curved in a substantially circular arc.